1. Field of the Invention
The present invention relates to a system for processing objects.
2. Description of the Related Art
Semiconductor devices are manufactured by performing a number of processes on semiconductor wafers (hereinafter referred to as "wafers") to a number of processes. To save space in the factory, the processing systems are laid out in the best possible manner. For the same purpose, the conveyer units designed to convey wafers from one process unit to another and the interfaces connecting the processing systems are made as small as possible. Further, to enhance the throughput of manufacture, it is necessary to convey wafers at the highest efficiency possible.
FIG. 1 shows a conventional resist-processing system which is designed to form a resist film on a wafer and to develop the resist film. As shown in FIG. 1, the system comprises a process unit A and an interface unit B. The process unit A has two convey paths 11 and 12 at its center section and two convey arms 13 and 14 provided in the convey paths 11 and 12, respectively. The process unit A further comprises an adhesion section, two baking section, a cooling section, two coating sections, and two development sections. The adhesion section and the first baking section are located on one side of the first convey path 11, and both coating sections on the other side thereof. The second baking section and the cooling section are arranged on one side of the second convey path 12, and both development sections on the other side thereof. (These sections are designated at the same reference numeral of "15."). The process unit A has a table 16 located between the convey paths 11 and 12, for holding wafers W that are to be conveyed from the process unit A to the interface unit B, or vice versa.
The interface unit B is positioned adjacent to the process unit A. The interface unit B is provided for transport wafers W between an exposure apparatus (not shown) and the process unit A. The interface unit B has an intermediate table 21, two buffer cassettes 22, a convey mechanism 23, a wafer-receiving table 24 and a wafer-sending table 25. The intermediate table 21 is located adjacent to the process unit A, can be moved up and down and can be cooled. The buffer cassettes 22 are provided on the sides of the intermediate table 21. The convey mechanism 23 is located at the back of the intermediate table 21 and can move along X, Y and Z axes and can rotate in the direction of arrow .theta.. The wafer-receiving table 24 and the wafer-sending table 25 are arranged farther from the intermediate table 21 than the convey mechanism 23. In other words, they are closer to the exposure apparatus (not shown) than the convey mechanism 23.
In operation, the first convey arm 13 conveys a wafer W onto the table 16, and the second convey arm 14 conveys the wafer W from the table 16 onto the intermediate table 21. The wafer W is cooled, if necessary, while mounted on the intermediate table 21. Thereafter, the convey mechanism 23 conveyers the wafer W from the intermediate table 21 onto the wafer-sending table 25. The wafer W is conveyed from the table 25 to the exposure apparatus (not shown).
A wafer W subjected to exposure process in the exposure apparatus is conveyed onto the wafer-receiving table 24. Then, the convey mechanism 23 conveys the wafer W from the table 24 onto the intermediate table 21. If wafers W are conveyed from the exposure apparatus to the resist-processing system at a higher rate than from the resist-processing system to the exposure apparatus, wafers W will be kept stored temporarily in the buffer cassettes 22.
A wafer W not exposed to light yet may rest on the intermediate table 21, while a wafer W already exposed to light rests on the wafer-receiving table 24. In this instance, the convey mechanism 23 conveys the unexposed wafer W from the intermediate table 21 into the buffer cassettes 22. Then, the mechanism 23 is moved to the wafer-receiving table 24, takes the exposed wafer W from the table 24, is moves back to the intermediate table 21, and places the exposed wafer W on the table 21. Next, the mechanism 23 is moved to the buffer cassettes 22, takes the unexposed wafer W out of the cassette 22 and mounts it on the wafer-sending table 25. This done, the convey mechanism 23 is moved to the intermediate table 21 and stays there until another unexposed wafer W is placed on the table 21.
The convey mechanism 23 needs to move twice to the buffer cassettes 22 in order to convey each unexposed wafer W to the wafer-sending table 25. Obviously, it takes longer to convey the unexposed wafer W to the table 25 than in the case where the mechanism 23 needs to move only once to the cassette 11. To make matters worse, the mechanism 23 cannot convey the next wafer unless no wafers are mounted on the intermediate table 21.
An example of the interface unit B is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-318247. The interface unit disclosed the publication cannot work if the process unit A has only one convey through which wafers W are conveyed toward or from the process unit A. Since the interface unit has no buffer cassettes, time is wasted when the timing of conveying wafers in the process unit A greatly differs from the timing of conveying wafers between the interface unit B and the exposure apparatus.